February 6, 2014
By Jim Moore
The FAA announced on Feb. 5 a new policy that could significantly reduce the cost of installing an angle of attack indicator in certificated aircraft. These devices have been identified by the General Aviation Joint Steering Committee (on which the AOPA Foundation's Air Safety Institute serves as co-chair) as the most effective system available for reducing loss-of-control accidents, and low-cost models have been installed by experimental aircraft operators for many years. The cost of obtaining required approvals to certify the devices for certificated aircraft has remained a barrier to widespread use, and the new policy will allow manufacturers to secure FAA approval through a letter of authorization, rather than the more complicated (and expensive) process of obtaining a technical standard order (TSO) or parts manufacturer authorization (PMA). Manufacturers will now be allowed to submit documentation that a given device complies with an ASTM International standard that was developed by industry.
In the absence of an angle of attack indicator, pilots are taught to avoid stalls primarily by maintaining sufficient airspeed, though airspeed and angle of attack are not actually related: an airplane can stall at any airspeed, any attitude, and any power setting. An analysis of accident data from 2001 to 2010 by a steering committee working group (also led by AOPA) found 40 percent of fatal accidents during that period had loss of control as a cause.
“We have eliminated major barriers so pilots can add another valuable cockpit aid for safety,” said FAA Administrator Michael Huerta in a press release. “These indicators provide precise information to the pilot, and could help many avoid needless accidents.”
A standards-based approval process could have a significant positive effect on safety, and may be applied to other add-on systems and technologies as well, the FAA noted. Maximizing installations and realizing the full potential of angle of attack indicators to save lives will depend on how the approval process is implemented, and the FAA noted in its press release that the Aircraft Certification Office in Chicago will process all applications to ensure a consistent interpretation of the new policy.
There remain some limits on retrofitting certificated aircraft with angle of attack indicator systems under the new policy: They must be installed as stand-alone systems, independent of other instruments and controls. While there is a provision for connecting to the aircraft’s electrical power system, the FAA will require that the devices be placarded “not for use as a primary instrument for flight,” and will not allow installations that allow the device to transmit data to, or receive it from, other aircraft instruments and controls. The new policy also prohibits installation of the angle of attack indicator in a place that will obstruct the pilot’s view or cause distraction. In many installations, the instrument is positioned prominently on the glareshield, a position that calls attention to the critical information it delivers and maximizes its utility. It remains to be seen if the policy will be interpreted to allow such installations.
Angle of attack indicators offer benefits beyond stall avoidance: They can also help pilots fly more efficiently by clearly indicating that wings are operating at maximum efficiency during the various phases of a flight. Like stall speed, other key airspeeds can vary with changes in weight, air temperature, and air density, while the angle of attack associated with a given phase, such as VX, VY, or VA, is consistent. A direct indication of angle of attack can also increase cruise efficiency, indicating the aerodynamic performance of the wing and allowing pilots to adjust for minimum drag.
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